The present invention relates to a new and improved construction of an embroidery machine.
In its more particular aspects, the present invention relates specifically to a new and improved construction of an embroidery machine comprising an embroidery framework which is displaceable essentially both in vertical and horizontal directions by related drive means defining respective vertical and horizontal drives. The embroidery framework contains a circumferentially closed embroidery frame which is supported at supports which are substantially vertically displaceable by the vertical drive. The horizontal drive acts upon at least one side member of the embroidery frame.
Due to the great length of embroidery machines and thus of the embroidery framework there repeatedly result problems with respect to the dimensional stability or rigidity of the embroidery framework, particularly since the relatively short-stroke displacing movements of the embroidery framework should have the same magnitude at each location of the embroidery framework in order to prevent inaccurate or distorted embroidery patterns or designs.
Embroidery frameworks and more particularly such embroidery frameworks of great length and provided with cloth beams which are arranged above each other in a plural number of decks, have a large mass which must be displaced with rapidly successive displacing movements during an embroidering operation. There result therefrom in hitherto known embroidery machines distortion phenomena or warping in the plane of the embroidery framework, particularly so-called parallelogram displacements, that is angular displacements at the corner or apex connections of the circumferentially closed embroidery frame. Such distortion phenomena or warping, above all, occur because the element which transmits the horizontal displacement to the framework and which usually comprises one or two horizontally and parallelly extending tooth racks or the like, always remains at the same level with respect to the stationary machine stand, while the embroidery framework, contrary thereto, is located higher or lower depending on the progress of the embroidering operation. Thus, the point of engagement for initiating the horizontal displacement is continuously displaced relative to the mass center of the embroidery framework or, respectively, relative to the upper and lower horizontal frame members which transmit the horizontal displacement. Due to this effect and depending on the position of the embroidery framework, smaller or greater angular dislocations occur. The parallel arrangement of two elements, for example, tooth racks or the like, one above the other for initiating the horizontal drive at one side member of the embroidery frame, may possibly somewhat diminish the disadvantages of the aforementioned parallelogram displacements but cannot totally remove such disadvantages.
It may be obvious to increase the dimensional stability or rigidity of the embroidery frame by substantially reinforcing the corner or apex connections thereof. Such measures, however, would necessarily result in a further increase of the weight or mass of the embroidery framework. Such weight or mass increase, in turn, would result in unbearable loads on the drive means, particularly at the presently desired high embroidering speeds.